Practically all gas turbine engines utilize labyrinth seals throughout the engine to restrict or to prevent the flow of gas or fluids between adjacent internal compartments of the engine. Such labyrinth seal system is demonstrated by U.S. Pat. No. 3,989,410 issued Nov. 2, 1976 to Bartolomeo Joseph Ferrari of Topsfield, Mass., and assigned to the assignee of the present application, and is incorporated herein by reference. Such referenced patent in its single figure which is a partial cross-sectional view of a typical aircraft gas turbine engine illustrates several labyrinth seals in their practical applications where they are installed to control by throttling the gas or fluid flow between adjacent compartments through a series of annular constrictions formed by the radial clearance at the tips of their labyrinth teeth.
It is well known that there is a great deal of difficulty involved in the controlling of the magnitude of such radial clearances due to the large deflections imposed by thermal gradients, centrifugal and gas pressure forces, shaft flexing, etc. For these reasons, most of the applied designs of labyrinth seals permit excessive leakage of the gas or fluid between the adjacent compartments which they are intended to seal against leakage. Such undesirable leakage through the seals has a negative affect on engine efficiency, performance, fuel burn and also on turbine temperature. For example, when the labyrinth seals are used as gas buffers, to control leakage of lubrication from shaft bearing compartments, excessive leakage has the affect of raising oil heat load and increasing oil to fuel heat exchanger size and weight, because the heat from the normally hotter pressurizing air is absorbed by the lubricant. Weight and efficiency of lubrication compartment air-oil separator systems are also adversely affected, because of the requirement to handle greater volume flow rates of air.
There are many other applications where labyrinth seals are used as dynamic seals, such as pumps for handling toxic gases or gases otherwise harmful to the environment, or where expensive process gases have to be sealed. It is clearly obvious in all the above-mentioned exemplary application areas, that it is very important to limit or eliminate seal leakage rates.